Atomization Characteristics for Various Ambient Pressure of Dimethyl Ether (DME)

Recently, dimethyl ether (DME) has been attracting much attention as a clean alternative fuel, since the thermal efficiency of DME powered diesel engine is comparable to diesel fuel operation and soot free combustion can be achieved. In this experiment, the effect of ambient pressure on DME spray was investigated with observation of droplet size such as Sauter mean diameter (SMD) by the shadowgraph and image processing method. The higher ambient pressure obstructs the growth of DME spray, therefore faster breakup was occurred, and liquid column was thicker with increasing the ambient pressure. Then engine performances and exhaust emissions characteristics of DME diesel engine were investigated with various compression ratios. The minimum compression ratio for the easy start and stable operation was obtained at compression ratio of about 12. The brake thermal efficiencies with various compression ratio from 12 to 17.7 (original compression ratio) were almost same level when compared to the original compression ratio of the engine. When the engine fueled with DME is operated at low compression ratio, the theoretical thermal efficiency decrease. However, the high combustion efficiency, the increased degree of constant volume and the lower heat loss to cooling water make up for the decreased theoretical thermal efficiency. Furthermore, the low THC and CO emissions and engine noise were comparable to original compression ratio, and the reduction of NOx emission was achieved.